It is common practice to inspect workpieces subsequent to production on a coordinate positioning apparatus, such as a coordinate measuring machine having a movable probe head within a working volume of the machine.
In a conventional 3-D measurement machine, the probe head is supported for movement along three mutually perpendicular axes (in directions X, Y and Z). Thereby, the probe head can be guided to any arbitrary point within the working volume of the measuring device.
Stationary measuring devices for measuring local structures such as cylindrical cavities are known from prior art. These machines allow accurate measurement of local structures of an object. However, the measuring rate of measuring machines of this kind is conventionally very low. Additionally, this type of coordinate measuring machine usually can only be used stationarily—the respective object to be measured has to be brought to the measuring machine. These machines, therefore, cannot be used for measuring structures of particularly large objects, for example boreholes in aircraft assembly parts, such as the fuselage or the wings. A hand held coordinate measuring device for the measuring of cavities is disclosed, for example, in EP 1 797 813. This document describes an optical measuring device for measuring the inner wall of a cavity formed in an object according to the confocal imaging principle. A weakness of the described solution is the rather imprecise positioning and orientation of the hand held device during the measurement. Though adaptation means with mechanical coupling elements for a defined positioning of the device during the measurement are disclosed, these cannot eliminate measurement errors caused by holes not orthogonal to the surface of the object or unevenly shaped surfaces.